1. Field of the Invention
This invention relates to digital communication systems and, more particularly, to synchronizing arrangements employed therein.
2. Description of the Prior Art
A digital data communication system such as a time-division multiplexing system typically includes arrangements situated at various points throughout to achieve bit synchronization of the digital data processed by the system. The digital data generally consists of a plurality of "words" of information, a "word" comprising a number of bits handled as a unit by the system. For a given format there are usually a fixed number of bits in each word. Frequently, a predetermined number of words constitutes a "frame" of data. Thus the nomenclature given the digital data often depends upon where the data are located within the system. To obviate such semantical hindrances and to particularize the broad utility of my invention, the more general phrase "bit stream" will be used hereinafter to describe a plurality of bits wherever the bits are located in the system.
In one type synchronization arrangement it is known to interpose a prefixed synchronizing bit sequence in the bit stream. A synchronizer detects the presence or absence of the prefixed sequence and determines that synchronization either has been achieved or is absent in response thereto.
A second type synchronization arrangement, to which the present invention pertains, includes apparatus for advantageously comparing two bit streams. Known comparison bit stream synchronizers usually store one bit stream in a buffer and compare a second bit stream bit-by-bit against the first bit stream. When a predetermined number of consecutive bits match, synchronization is assumed to have been achieved. Otherwise, synchronization is assumed to be absent.
Thus, in monitoring a plurality of bit streams a synchronizer has at least two functions: (1) to achieve synchronization and (2) to detect the absence of synchronization among the bit streams. Unfortunately, known synchronizers are inefficient with respect to the time required for accomplishing these functions.
Accordingly, an object of my invention is to provide a digital bit stream synchronizer which reduces the time for achieving synchronization among a plurality of bit streams.